/* Copyright � 2002-2011 by Aidant Systems, Inc., and by Jason Smith. */

using System.Collections;

namespace Spring.Collections.Generic;

/// <summary>
/// <p>Implements an immutable (read-only) <c>Set</c> wrapper.</p>
/// <p>Although this is advertised as immutable, it really isn't.  Anyone with access to the
/// <c>basisSet</c> can still change the data-set.  So <c>GetHashCode()</c> is not implemented
/// for this <c>Set</c>, as is the case for all <c>Set</c> implementations in this library.
/// This design decision was based on the efficiency of not having to <c>Clone()</c> the
/// <c>basisSet</c> every time you wrap a mutable <c>Set</c>.</p>
/// </summary>
[Serializable]
public sealed class ImmutableSet<T> : Set<T>
{
    private const string ERROR_MESSAGE = "Object is immutable.";
    private ISet<T> mBasisSet;

    internal ISet<T> BasisSet
    {
        get { return mBasisSet; }
    }

    /// <summary>
    /// Constructs an immutable (read-only) <c>Set</c> wrapper.
    /// </summary>
    /// <param name="basisSet">The <c>Set</c> that is wrapped.</param>
    public ImmutableSet(ISet<T> basisSet)
    {
        mBasisSet = basisSet;
    }

    /// <summary>
    /// Adds the specified element to this set if it is not already present.
    /// </summary>
    /// <param name="o">The object to add to the set.</param>
    /// <returns>nothing</returns>
    /// <exception cref="NotSupportedException"> is always thrown</exception>
    public override sealed bool Add(T o)
    {
        throw new NotSupportedException(ERROR_MESSAGE);
    }

    /// <summary>
    /// Adds all the elements in the specified collection to the set if they are not already present.
    /// </summary>
    /// <param name="c">A collection of objects to add to the set.</param>
    /// <returns>nothing</returns>
    /// <exception cref="NotSupportedException"> is always thrown</exception>
    public override sealed bool AddAll(ICollection<T> c)
    {
        throw new NotSupportedException(ERROR_MESSAGE);
    }

    /// <summary>
    /// Removes all objects from the set.
    /// </summary>
    /// <exception cref="NotSupportedException"> is always thrown</exception>
    public override sealed void Clear()
    {
        throw new NotSupportedException(ERROR_MESSAGE);
    }

    /// <summary>
    /// Returns <see langword="true" /> if this set contains the specified element.
    /// </summary>
    /// <param name="o">The element to look for.</param>
    /// <returns><see langword="true" /> if this set contains the specified element, <see langword="false" /> otherwise.</returns>
    public override sealed bool Contains(T o)
    {
        return mBasisSet.Contains(o);
    }

    /// <summary>
    /// Returns <see langword="true" /> if the set contains all the elements in the specified collection.
    /// </summary>
    /// <param name="c">A collection of objects.</param>
    /// <returns><see langword="true" /> if the set contains all the elements in the specified collection, <see langword="false" /> otherwise.</returns>
    public override sealed bool ContainsAll(ICollection<T> c)
    {
        return mBasisSet.ContainsAll(c);
    }

    /// <summary>
    /// Returns <see langword="true" /> if this set contains no elements.
    /// </summary>
    public override sealed bool IsEmpty
    {
        get { return mBasisSet.IsEmpty; }
    }

    /// <summary>
    /// Removes the specified element from the set.
    /// </summary>
    /// <param name="o">The element to be removed.</param>
    /// <returns>nothing</returns>
    /// <exception cref="NotSupportedException"> is always thrown</exception>
    public override sealed bool Remove(T o)
    {
        throw new NotSupportedException(ERROR_MESSAGE);
    }

    /// <summary>
    /// Remove all the specified elements from this set, if they exist in this set.
    /// </summary>
    /// <param name="c">A collection of elements to remove.</param>
    /// <returns>nothing</returns>
    /// <exception cref="NotSupportedException"> is always thrown</exception>
    public override sealed bool RemoveAll(ICollection<T> c)
    {
        throw new NotSupportedException(ERROR_MESSAGE);
    }

    /// <summary>
    /// Retains only the elements in this set that are contained in the specified collection.
    /// </summary>
    /// <param name="c">Collection that defines the set of elements to be retained.</param>
    /// <returns>nothing</returns>
    /// <exception cref="NotSupportedException"> is always thrown</exception>
    public override sealed bool RetainAll(ICollection<T> c)
    {
        throw new NotSupportedException(ERROR_MESSAGE);
    }

    /// <summary>
    /// Copies the elements in the <c>Set</c> to an array of T. The type of array needs
    /// to be compatible with the objects in the <c>Set</c>, obviously.
    /// </summary>
    /// <param name="array">An array that will be the target of the copy operation.</param>
    /// <param name="index">The zero-based index where copying will start.</param>
    public override sealed void CopyTo(T[] array, int index)
    {
        mBasisSet.CopyTo(array, index);
    }

    /// <summary>
    /// The number of elements contained in this collection.
    /// </summary>
    public override sealed int Count
    {
        get { return mBasisSet.Count; }
    }

    /// <summary>
    /// Returns an object that can be used to synchronize use of the <c>Set</c> across threads.
    /// </summary>
    public override sealed bool IsSynchronized
    {
        get { return ((ICollection) mBasisSet).IsSynchronized; }
    }

    /// <summary>
    /// Returns an object that can be used to synchronize the <c>Set</c> between threads.
    /// </summary>
    public override sealed object SyncRoot
    {
        get { return ((ICollection) mBasisSet).SyncRoot; }
    }

    /// <summary>
    /// Gets an enumerator for the elements in the <c>Set</c>.
    /// </summary>
    /// <returns>An <c>IEnumerator</c> over the elements in the <c>Set</c>.</returns>
    public override sealed IEnumerator<T> GetEnumerator()
    {
        return mBasisSet.GetEnumerator();
    }

    /// <summary>
    /// Returns a clone of the <c>Set</c> instance.
    /// </summary>
    /// <returns>A clone of this object.</returns>
    public override sealed object Clone()
    {
        return new ImmutableSet<T>(mBasisSet);
    }

    /// <summary>
    /// Performs a "union" of the two sets, where all the elements
    /// in both sets are present.  That is, the element is included if it is in either <c>a</c> or <c>b</c>.
    /// Neither this set nor the input set are modified during the operation.  The return value
    /// is a <c>Clone()</c> of this set with the extra elements added in.
    /// </summary>
    /// <param name="a">A collection of elements.</param>
    /// <returns>A new <c>Set</c> containing the union of this <c>Set</c> with the specified collection.
    /// Neither of the input objects is modified by the union.</returns>
    public override sealed ISet<T> Union(ISet<T> a)
    {
        ISet<T> m = GetUltimateBasisSet();
        return new ImmutableSet<T>(m.Union(a));
    }

    /// <summary>
    /// Performs an "intersection" of the two sets, where only the elements
    /// that are present in both sets remain.  That is, the element is included if it exists in
    /// both sets.  The <c>Intersect()</c> operation does not modify the input sets.  It returns
    /// a <c>Clone()</c> of this set with the appropriate elements removed.
    /// </summary>
    /// <param name="a">A set of elements.</param>
    /// <returns>The intersection of this set with <c>a</c>.</returns>
    public override sealed ISet<T> Intersect(ISet<T> a)
    {
        ISet<T> m = GetUltimateBasisSet();
        return new ImmutableSet<T>(m.Intersect(a));
    }

    /// <summary>
    /// Performs a "minus" of set <c>b</c> from set <c>a</c>.  This returns a set of all
    /// the elements in set <c>a</c>, removing the elements that are also in set <c>b</c>.
    /// The original sets are not modified during this operation.  The result set is a <c>Clone()</c>
    /// of this <c>Set</c> containing the elements from the operation.
    /// </summary>
    /// <param name="a">A set of elements.</param>
    /// <returns>A set containing the elements from this set with the elements in <c>a</c> removed.</returns>
    public override sealed ISet<T> Minus(ISet<T> a)
    {
        ISet<T> m = GetUltimateBasisSet();
        return new ImmutableSet<T>(m.Minus(a));
    }

    /// <summary>
    /// Performs an "exclusive-or" of the two sets, keeping only the elements that
    /// are in one of the sets, but not in both.  The original sets are not modified
    /// during this operation.  The result set is a <c>Clone()</c> of this set containing
    /// the elements from the exclusive-or operation.
    /// </summary>
    /// <param name="a">A set of elements.</param>
    /// <returns>A set containing the result of <c>a ^ b</c>.</returns>
    public override sealed ISet<T> ExclusiveOr(ISet<T> a)
    {
        ISet<T> m = GetUltimateBasisSet();
        return new ImmutableSet<T>(m.ExclusiveOr(a));
    }

    /// <summary>
    /// Indicates that the given instance is read-only
    /// </summary>
    public override sealed bool IsReadOnly
    {
        get { return true; }
    }

    /// <summary>
    /// Performs CopyTo when called trhough non-generic ISet (ICollection) interface
    /// </summary>
    /// <param name="array"></param>
    /// <param name="index"></param>
    protected override void NonGenericCopyTo(Array array, int index)
    {
        ((ICollection) this.BasisSet).CopyTo(array, index);
    }

    /// <summary>
    /// Performs Union when called trhough non-generic ISet interface
    /// </summary>
    /// <param name="a"></param>
    /// <returns></returns>
    protected override sealed ISet NonGenericUnion(ISet a)
    {
        ISet<T> m = GetUltimateBasisSet();
        return new ImmutableSet(((ISet) m).Union(a));
    }

    /// <summary>
    /// Performs Minus when called trhough non-generic ISet interface
    /// </summary>
    /// <param name="a"></param>
    /// <returns></returns>
    protected override sealed ISet NonGenericMinus(ISet a)
    {
        ISet<T> m = GetUltimateBasisSet();
        return new ImmutableSet(((ISet) m).Minus(a));
    }

    /// <summary>
    /// Performs Intersect when called trhough non-generic ISet interface
    /// </summary>
    /// <param name="a"></param>
    /// <returns></returns>
    protected override sealed ISet NonGenericIntersect(ISet a)
    {
        ISet<T> m = GetUltimateBasisSet();
        return new ImmutableSet(((ISet) m).Intersect(a));
    }

    /// <summary>
    /// Performs ExclusiveOr when called trhough non-generic ISet interface
    /// </summary>
    /// <param name="a"></param>
    /// <returns></returns>
    protected override sealed ISet NonGenericExclusiveOr(ISet a)
    {
        ISet<T> m = GetUltimateBasisSet();
        return new ImmutableSet(((ISet) m).ExclusiveOr(a));
    }

    private ISet<T> GetUltimateBasisSet()
    {
        ISet<T> m = this.mBasisSet;
        while (m is ImmutableSet<T>)
            m = ((ImmutableSet<T>) m).mBasisSet;
        return m;
    }
}
